1. Field of the Invention
The invention relates to apparatus for removing moisture from a gas, and in particular, to a moisture removal apparatus for a compressed air line, having a series of moisture traps including a renewable desiccant material. The desiccant material is contained in an easily replaced canister having means to retain the desiccant when the canister is removed for rejuvenation, for example by baking.
2. Prior Art
It is often desirable to provide air or other gases having relatively low humidity for use in a device or a process. One example is a compressed air supply for a spray painting process, where it is necessary to ensure that no water becomes mixed with the paint. It is especially important to remove water droplets from the air supply, and inasmuch as pressure changes along a flow path can produce condensation, it is desirable to ensure a low relative humidity. Many devices are known for removing water from gaseous fluids. Such devices are generally one of two types. One type relies on the pattern and velocity of the gas flowing through the device to cause water droplets to accumulate at a particular trap area within the device. The water droplets are extracted, for example, at a reversal of the flow path directing droplets into a trap, and the trap can be drained via a valve. Such a device removes droplets but does not reduce the humidity of the gas.
The other type of moisture removal device passes the gas through a body of material which absorbs water. Filter pads can accumulate water in capillary passages defined between fibers, or a desiccant material can be provided to remove moisture from the passing gas. These dryers eventually become saturated with water, but can be rejuvenated by heating the material to a high enough temperature to drive off the moisture. Desiccant type dryers having a replaceable canister containing desiccant material are known. When the desiccant becomes saturated, the canister is typically removed and returned to a regeneration facility, and replaced by a canister containing fresh desiccant material. The regeneration facility typically reloads the returned canister with fresh desiccant, and so on.
An absorptive or desiccant dryer typically has a connection head including an inlet and an outlet for relatively permanent mounting in a fluid flow system. A desiccant-containing canister having an inlet and an outlet is removably attached to the head. The canister is generally cylindrical in shape, and in order to provide a large area of contact and minimal flow restriction the desiccant fills an annular space between an inner wall of the canister and a central passageway. The central passageway is perforated over its length and leads to the inlet or outlet. Gas flows from the connection head into the canister, and partially through the desiccant material, exiting the central passageway at any point along its perforated length. Known desiccant dryers do not efficiently utilize the desiccant material because all the gas is not forced to flow through the entire desiccant bed. Instead, the length of the flow path through the desiccant bed varies with the point at which the gas passes between the desiccant and the perforated central passageway or tube.
The present invention provides a desiccant type dryer in a moisture removal apparatus, the desiccant portion having a replaceable canister containing renewable desiccant material captured between an end screen, the wall of the canister and a tube having openings distributed at one end of the tube. The end screen and the opposite end of the tube communicate with the inlet and outlet via particular seal structures associated with the canister top, defining a flow path for the gas which causes all the gas to flow through the entire length of the desiccant bed in the canister. The desiccant dryer is preferably provided as an element in series with a non-absorptive coalescent filter element as disclosed in U.S. Pat. No. 4,822,387, which is hereby incorporated, and in series with a pad-type absorptive filter. The apparatus effectively removes water droplets and water vapor, and is particularly useful for high performance applications such as spray painting and other critical pneumatic systems that cannot tolerate moisture contamination.